New Publications are available for F-region
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New Publications are available now online for this publication.
Please follow the links to view the publication.Satellite diagnostics of the northern ionosphere and measurements of the HF signal angles of arrival
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0040
The main ionospheric trough can be formed as result of horizontal convection and field-aligned plasma transport, changes in the electric and magnetic fields, precipitation of electrons, interaction of ionospheric plasma with neutral components and recombination and ionisation processes occurring in the ionosphere and inner magnetosphere. Recently the position of the minimum, and poleward and equatorward edges of the main ionospheric trough has been determined by a hybrid method based on wave diagnostics across the whole frequency band, together with electron and density temperature measurements. For terrestrial HF systems, the electron density depletion in the trough region reduces the maximum frequency that can be reflected by the ionosphere along the great circle (GC) path. The gradients in electron density associated with the trough walls and embedded ionospheric irregularities often result in propagation in which the signal path is well displaced from the GC direction with directions of arrival (DOA) at the receiver offset by up to 100°. Deviations from the GC direction impact not only on radiolocation systems for which estimates of a transmitter location are obtained by triangulation from a number of receiving sites, but also on any radio communications system in which directional antennas are employed. In this paper, in order to determine the mechanisms that are responsible for the off GC behaviour described above, HF signals propagating along the Uppsala-Leicester path are examined in the context of DEMETER observations of electron density structure and particle precipitation in the ionospheric trough region for a number of case studies.Variations of HF signal propagation characteristics over mid-latitude paths during magnetic storms: experiment and modelling
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0080
This work studies variations of HF characteristics and ionospheric parameters recorded over mid-latitude paths of Russian East-Siberian region during magnetic storms on May 15, 1997, and September 24, 2006. The sharp wave-like changes of maximum observed frequencies (MOF) were recorded during the main phase of investigated storms. Assuming that observed MOF variations can be produced by ionospheric disturbances propagating from the northern to the southern latitudes simulation of HF propagation conditions was carried out.The equatorial scintillations and space weather effects on its generation during geomagnetic storms
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0071
Great diversity of the ionospheric phenomena leads to a variety of irregularity types with spatial size from many thousands of kilometers to few centimeters and lifetimes from days to fractions of second. Since the ionosphere strongly influences the propagation of radio waves, signal distortions caused by these irregularities affect short-wave transmissions on Earth, transionospheric satellite communications and navigation. In this work the solar wind and the equatorial ionosphere parameters, Kp, Dst, AU, AL indices characterized contribution of different magnetospheric and ionospheric currents to the H-component of geomagnetic field are examined to test the space weather effect on the generation of ionospheric irregularities producing VLF scintillations. According to the results of the current statistical studies, one can predict scintillations from Aarons' criteria using the Dst index, which mainly depicts the magnetospheric ring current field. To amplify Aarons' criteria or to propose new criteria for predicting scintillation characteristics is the question. In the present phase of the experimental investigations of electron density irregularities in the ionosphere new ways are opened up because observations in the interaction between the solar wind-magnetosphere-ionosphere during magnetic storms have progressed greatly. We have examined scintillation relation to magnetospheric and ionospheric currents and show that the factor, which presents during magnetic storms to fully inhibit scintillation, is the positive Bz-component of the IMF. During the positive Bz IMF F layer cannot raise altitude where scintillations are formed. The auroral indices and Kp do better for the prediction of the ionospheric scintillations at the equator. The interplanetary magnetic field data and models can be used to explain the relationship between the equatorial ionospheric parameters, h'F, f<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">0</sub>F2, and the equatorial geomagnetic variations with the polar ionosphere currents and the solar wind. Taking into account the time delay between the solar wind and the ionosphere phenomena, the relationship between the solar wind and the ionosphere parameters can be used for predicting of scintillations.Seismic traveling ionosphere irregularities at F2-region in time of heliogeophysic disturbances on data of distance sounding
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0089
The properties of traveling ionosphere disturbances (TID) (their horizontal sizes are 1-4 thousand kms, excesses of a background are 15-30 %), formed in F2 layer as a result of strong earthquake in time of heliogeophysical perturbations are explored. The irregularities arise 10-15 h before earthquakes and move horizontally with a transonic speed on distances of a few thousand kms up to round - the - world trajectories focused approximately along an arc of a major circle, transiting above epicenter region. Information of spent examination was caused by spatial - time differences of dynamics of F2-layer of an ionosphere in time of the heliogeophysical disturbances from dynamics of quasi- causative seismic macro-scale ionosphere irregularities.A model for time and frequency spreading of HF radio signals propagating through the equatorial ionosphere
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060248
An essential part of a method for the prediction of reliability of a digital communication system at HF, is the inclusion of a model for post-sunset scattering of signals in both the time and frequency domains. Although models have been developed for trans-ionospheric scintillation, little quantitative data is available for terrestrial systems. This paper proposes a model and indicates a procedure for the inclusion of scattering in the estimation of reliability.Satellite radiosounding of the ionosphere from heights near to a maximum of F2 layer
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060298
The generalized results and experience in the field of carrying out the experiments on the ionosphere radio sounding at the "MIR" manned space station (heights 340-390 km) are presented and analyzed. New multi frequency paths for radio wave propagation between the satellite and Earth, new data about the local specific macro irregularity in ionosphere and an adaptation of the IRI model by experimental data and some other factors were shown.Existence of an additional layer in equatorial ionosphere: other observations
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060280
In this paper we present an observation of an additional layer over the Malaysian ionosphere using bottomside sounding. This F3 layer has been observed over Brazil by Balan et al., (1995). Other work done by Uemoto et al., (2004) from the observation of topside sounding obtained by the Ohzora satellite confirmed this work. In Malaysia, the layer has been observed at the newly established ionosonde station at Batu Pahat (lat. 1° 86' N, long. 103° 8' E). This station has been in operation since October 2004. Continuous sweep soundings are made every 15 minutes along with single frequency soundings. Greatest appearance of the F3-layer is around local noon while the least is after local dawn. The mean height for the layer is about 600 km reaching a maximum of about 900 km during the months of Nov, 2004 Jan, 2005. This period is in agreement with the occurrence of F3 layer observed by Balan et al. work (December solstices). It is seen that the critical frequency of the F2 layer decreases with the appearance of the F3-layer. This phenomena can be attributed to the equatorial anomaly and the upward neutral wind and E × B drift.Case studies of enhanced E-layer formation at high-latitudes following sudden commencement absorption events
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060242
This paper examines the formation of an enhanced E-layer that blankets the F-layer following sudden commencement absorption (SCA) events. Our case studies illustrate that storm sudden commencement (SSC) events cause impulsive precipitation of the otherwise trapped high energy electron population and that the precipitation of these high energy electrons may create considerable but short lived electron density enhancements (ionisation) at all ionospheric altitudes and particularly in the D and E layers (60-120 km altitude). The effect on HF communication links is demonstrated.Evaluation of the IRI model efficiency for operational forecast of HF propagation conditions
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060279
New approaches for adaptation of the international reference ionosphere model IRI to current ionospheric parameters are used to improve the determination of maximum usable frequency was given. MUF and path length D for HF waves propagated via the ionosphere with an example of one European path. Parameters foF2 (maximum frequency of the F2 layer) and TEC (total electron content) are used as adaptive ones. In additional the analytical approximation is proposed for the IRI model residual error. Its influence on MUF and D errors is given.Modelling of returned trajectories at heights below the maximum of the F2 layer
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060283
Radiosounding experiments aboard the "Mir" manned space station resulted in ionograms with retarded lower traces (RLT) (N.P. Danilkin, 2001). These unique traces can be explained as traces of trajectories which are irradiated from a satellite and after an inclined reflection from Earth come back to the satellite as a result of their sharp deviation by the irregularity in the ionosphere (returned trajectories). These trajectories require detailed research, which can be achieved by means of mathematical modeling. By varying positions of the satellite and the irregularity, it is possible to define optimal conditions of getting such trajectories in process of transionospheric radiosounding. The results of such an analysis are presented in the paper. Haselgrove method of ray tracing, also known as the method of characteristics was used (J. Haselgrove, 1955). The characteristic differential equations were handled by the method of Runge-Kutte. The detailed classification of calculated returned trajectories is presented in the paper, the dependence of each trajectory type on the position of the satellite and irregularity relative to each other and relative to the maximum of the F2 layer is shown.Inverse problems of ionospheric radiosounding at heights below the maximum of the F2 layer
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060277
The Tikhonov method of mathematical modelling is suggested for the solution of inverse problems of transionospheric radiosounding at heights below the maximum of the F2 layer and in cases of retarded lower traces (RLT).The simulation of HF off-great circle propagation effects due to large scale electron density structures within the polar cap and due to the mid-latitude trough
http://dl-live.theiet.org/content/conferences/10.1049/cp_20030465
Observations over recent years have established that large scale electron density structures are a common feature of the polar cap F-region ionosphere. Whilst experimental work has produced many useful results (Warrington, E.M. et al., IEE Proc. on Microwaves, Antennas and Propag., vol.144, p.241-9, 1997; Rogers, N.C. et al., IEE Proc. on Microwaves, Antennas and Propag., 2003; vol.144, p.91-6, 1997), they were obtained for a small number of paths and frequencies. In order to be able to develop tools to enable such effects to be considered in the design and operation of HF radio systems for which the signals impinge on the polar cap ionosphere, but for frequencies and paths not subject to experimental investigation, a ray tracing model has been developed. The results obtained from the ray tracing simulations are presented together with examples of experimental observations. However, it is well known that the high latitude ionosphere is an extremely complex HF propagation environment and, therefore, precise agreement between experiment and simulation has not been attempted and should not be expected.The simulation of off-great circle HF propagation effects
http://dl-live.theiet.org/content/conferences/10.1049/cp_20030033
Observations over recent years have established that large scale electron density structures are a common feature of the polar cap F-region ionosphere. These structures take the form of convecting patches and arcs of enhanced electron density which form tilted reflection surfaces for HF radiowaves, allowing off great circle propagation paths to be established. Numerical ray tracing has been employed to simulate the effects of these structures on the ray paths of the radiowaves. The simulations have reproduced the precise character of experimental observations of the direction of arrival over a propagation path within the polar cap and of oblique ionograms obtained over the same path.Nowcasting and forecasting the foF2, MUF(3000)F2 and TEC based on empirical models and real-time data
http://dl-live.theiet.org/content/conferences/10.1049/cp_20030035
This paper describes an interactive on-line procedure for nowcasting and forecasting the critical frequency of the ionospheric F2 layer f<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">0</sub>F2, the maximum usable frequency for a 3000 km range, MUF(3000)F2, and the total electron content TEC, based on empirical models and near real-time data initially developed under the EU COST 251 Action (Hanbaba, 1999). It has been recently improved in such a way as to be useful to radio users who need up-to-date information on ionospheric conditions over Europe to meet their operational requirements (Cander, 2003). In particular, the ability to provide and process prompt plasmaspheric and ionospheric data is improving with the aim to better characterise the geographic, temporal, seasonal, and solar cycle dependence of these potentially serious ionospheric effects on radio communication performance during severe space weather conditions. Extensive comparisons between measured and forecast values of f<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">0</sub>F2, MUF(3000)F2 and TEC from January 2000 to August 2002 have been conducted, as well as comparisons between automatic and manually scaled parameters. The merits are stressed of real-time use of data to provide more accurate specification of the ionospheric space weather and forecast its effects in the near future.Degradation in neural network prediction models of foF2 with time
http://dl-live.theiet.org/content/conferences/10.1049/cp_20010401
Ionospheric forecasting services fall short of the precision required for many practical applications. In-service models of ionospheric parameters often fail to offer much of an increase in performance over simple persistence or recurrence. In particular, predictions of storm events and disturbances are very poor. This performance shortfall can be attributed to several causes one of which is an inability to adequately model solar-magnetospheric-ionospheric physics. To circumvent this knowledge gap some authors have adopted knowledge independent (time-series) modelling techniques that can utilise typical ionospheric data sets. A number of experimental and theoretical studies have demonstrated the importance of non-linear behaviour within the solar-terrestrial environment. Attention has also turned to time series predictive methods derived from studies into artificial intelligence (AI) and the application of neural network (NN) based techniques to geophysical prediction problems. Francis et al. (2000) undertook a study of neural networks for the prediction of the ionospheric parameter f<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">0</sub>F2 based on the use of historical data from the 1970s. The resultant model for the one hour ahead prediction of this parameter had an RMS error of only ~0.4 MHz. A version of this model, but re-optimised, was incorporated in the Ionospheric Forecasting Demonstrator (IFD). However, it soon became clear that the predictive capability of the IFD was degrading with time. This paper reports on our studies to understand the reasons for this degradation and to improve the model.A comparison of methods for the measurement of ionospheric tilt from a topside ionospheric sounder
http://dl-live.theiet.org/content/conferences/10.1049/cp_20000180
This paper presents a comparison of the two main techniques for measuring the direction of arrival of signals that have been proposed for implementation on a topside sounding satellite. The assumption is that the topside sounder would be a payload on a Surrey Satellite Technology Limited (SSTL) satellite. The two candidate methods are amplitude direction finding (DF) where the relative amplitude on two (or more) receiving antennas is compared, and an interferometric method where the relative phases of reception on two antennas separated in space are compared. A novel interferometric “synthetic aperture” method (SARDF) for across track DF is reported for the first time in this paper. This method is particularly well suited for providing the pulse signal returns in a form suitable for along track synthetic aperture measurements. The two methods are compared using a simple information theoretic approach to assess how angular accuracy is limited with respect to signal to noise ratio, pulse length and ionospheric roughness.Nonlinear prediction of the hourly FOF2 time series and the nonlinear interpolation of missing points
http://dl-live.theiet.org/content/conferences/10.1049/ic_19990069
This paper proposes a novel technique for the prediction of solar-terrestrial data sets that contain a significant proportion of missing data points. A nonlinear interpolation technique is employed to assign values to gaps in a time series. It interpolates each missing point such that the error introduced into any specific predictive function is minimised. Radial basis function (RBF) neural networks (NN) are adopted for the purpose of prediction, and their advantages over their multi-layer perceptron (MLP) counterparts are outlined. This technique has general application in any instance where the effects of interpolation upon a given analysis process need to be minimised or a complete time series needs to be constructed from non-contiguous data. (5 pages)Short-term ionospheric forecasting over Europe
http://dl-live.theiet.org/content/conferences/10.1049/cp_19990025
An operational forecasting tool for the European region based on continuous monitoring of the ionosphere is available on the World Wide Web for interactive use (http://www.rcru.rl.ac.uk/iono/maps.htm). A network of 23 ground-based vertical incidence ionosondes provides the basic inputs for the region of interest (10°W-90°E, 30°-70°N). Measurements of foF2 and M(3000)F2 are sent by e-mail, mainly in the form of URSIGRAM messages as described in ITU-R Recommendation P.313. Data are currently updated every 24 hours, though not all ionosondes provide values over the week-ends. Forecasts and archive measurement maps of the critical frequency foF2 and the maximum usable frequency for a 3000 km range, MUF(3000)F2, are then produced for the area of interest. Comparisons between the maps derived from measured and forecast values have been conducted.Imaging and modelling of the main ionospheric trough using radio tomography
http://dl-live.theiet.org/content/conferences/10.1049/cp_19990048
Information derived from tomographic images has demonstrated the extreme variability of the ionosphere over the UK, with structures within the electron concentration usually associated with the auroral zone being found at UK latitudes under disturbed geomagnetic conditions. The tomographic images indicate that the main trough in the F-layer electron concentration is routinely present over the northern UK at nighttime. With an enhanced geomagnetic disturbance the progression of the trough to lower latitudes is evidenced, while extremely disturbed conditions result in the trough minimum being as far south as northern France. The applicability of the tomographic technique to the production of an ionospheric model, that includes the prominent main trough in the plasma electron concentration, has been demonstrated. Initial results indicate that the model shows potential for modelling an accurate representation of the main trough extending to some 30° in longitude from the location of the input data. Ray tracing through the resulting tomographic images and the model of the mid-latitude trough has direct applications for the near-real-time determination of radio propagation conditions.High frequency observations and characterizations of coherent backscatters from midlatitude E-region
http://dl-live.theiet.org/content/conferences/10.1049/cp_19971654
This paper presents the first results of an experiment carried out during the summer of 1996. The aim of this article is to characterize backscatter echoes from the low altitude ionosphere. The observations have been made using Nostradamus facility near Dreux (France), a monostatic HF radar made of biconic antennas array which cover a large HF band. The east-west orientation of the array allows a narrow beam in the south-north direction in order to cover an area in the E-region magnetic aspect sensitive backscatter. The observations are azimuthal sectors scanning from -20 to 20 degrees from the geographical north. Each scan was completed in about 2 minutes to get a high Doppler resolution. This study is of importance in the improvement of an HF radar and in the recognition of backscatters from the E-region because they can reduce the radar detection capacity.SCIPION: a flexible ionospheric digital sounder. Illustration of its capabilities for spatial coherence studies of Es and F regions
http://dl-live.theiet.org/content/conferences/10.1049/cp_19970754
SCIPION is a new state of the art digital sounder that has been developed by France Telecom-CNET for ionospheric monitoring and research. Extensive data processing using DSP technology has resulted in a low power, low cost and full featured system for both vertical and oblique soundings. SCIPION provides numerous sounding capabilities. In a standard mode of operation, the amplitude ionogram is displayed together with the full channel scattering function at each sounding frequency. Antenna diversity can be performed using up to 8 antennas for spatial coherence and drift measurements, with only one receiver needed. Furthermore, by means of the SCIPION system, impulse response sequences of the ionospheric transmission channel can be measured and stored, in order to be used for simulation purposes. In this paper the system is described and some illustrative examples of its capabilities obtained during actual experimental situations are shown. Particular attention is given to spatial coherence studies of the F and Es ionospheric layers. Results are presented from an experiment performed over a short link in Brittany. It can be concluded that, in this case, the received signal was coming from two distinct sporadic E layers having different vertical velocities with very closed group paths and Doppler shifts.HF guidance in the vicinity of F layer maximum during ionospheric disturbances
http://dl-live.theiet.org/content/conferences/10.1049/cp_19970378
In the regular ionosphere the main characteristics of short wave propagation are described by the geometric-optic approach and have been studied sufficiently well. The existence of irregularities and disturbances of different forms complicates the propagation picture determining the scattering and diffraction effects. Despite widespread investigations of ionosphere irregular structure and its influence on radioelectronic systems the role of irregularities in ionospheric propagation has not yet been established fully. In the report experiments on oblique chirp sounding of the ionosphere, where the guidance effect of the Pedersen mode in the disturbed ionosphere was discovered, are presented. A theoretical explanation of the observed phenomenon is given and opportunities for the use of this effect for diagnostics of irregular structure in the ionosphere are also discussed. (4 pages)A hierarchy moment approach to the analysis and forecasting of linear-nonlinear propagation
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961181
This work is concerned with a new method for extracting inbred linear-nonlinear coupled differential equations from multivariate discrete time series data and is applied to f<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">0</sub>F2 forecasting. It is assumed that the solution of the coupled ordinary differential equations can be represented as a multivariate Volterra functional expansion. A tractable hierarchy of moment equations is generated by operating on a suitably truncated Volterra functional expansion. The hierarchy facilitates the calculation of the coefficients of the coupled differential equations. A dynamic global mid-/high-magnetic latitude ionospheric model is developed which can characterise nonlinear phenomena such as period doubling and quenching occurrences. (7 pages)Review of COST 238 (PRIME) achievements
http://dl-live.theiet.org/content/conferences/10.1049/ic_19951275
COST 238 (prediction and retrospective ionospheric modelling over Europe-PRIME) was a four-year project sponsored by the European Commission initiated in March 1991 and involving some 72 research workers from 31 organisations in 17 countries. The objectives, embodied in the agreed Memorandum of Understanding were: “to develop techniques for using ionospheric sounding information taken from existing measuring equipment to generate improved models of the European ionosphere, needed to estimate ionospheric propagation effects on telecommunication systems”. The author considers some of the results. (6 pages)Half-century of radio probing of the ionosphere
http://dl-live.theiet.org/content/conferences/10.1049/cp_19950820
The history of ground-based vertical-incidence sounding of the ionosphere is outlined. The ionosonde network serves for the patrol of the quiet or disturbed state of the ionosphere. Duration of the ionosphere F region peak parameters disturbance is compared with total electron content quiet times and sudden ionospheric disturbances detected by radio signal deterioration.Determination of dispersive bandwidths characteristic for the propagation of HF pulses via the ionosphere
http://dl-live.theiet.org/content/conferences/10.1049/cp_19950386
Discusses the range of the dispersive bandwidths characteristic for HF pulses propagating through F region of the ionosphere as determined both by the simulation technique and the analysis of ionograms. It is found to be from 20-190 kHz. It is noticed that variation of the dispersive bandwidths from case to case of propagation is similar whether calculated or deduced from ionograms, although the results from the two methods, for particular pulses can differ up to 50%. A better agreement probably could be obtained if the simulation technique is applied to the determination of the second total derivative of the group path with respect to frequency, and if a ray path more realistic than mirror reflection ones are considered in calculations based on the ionogram analysis. The discrepancy between results obtained by the simulation technique and the analysis of ionograms for the E region pulse propagation, is under 10%. The best agreement is in the cases of the propagation via thick sporadic-E, because the mirror type reflection is present. (4 pages)Some recent measurements of the direction of arrival of HF signals propagated over a path tangential to the mid-latitude trough
http://dl-live.theiet.org/content/conferences/10.1049/cp_19950392
Horizontal electron density gradients (tilts) in the ionosphere are responsible for the deviation of HF (330 MHz) radiowaves from the normal great circle propagation path (GCP). The resulting deviations are often far in excess of the instrumental accuracy (~0.1°) of direction finding (DF) systems and can amount to errors of over 50° at high latitude sites where relatively large ionospheric tilts may occur. One region of the ionosphere in which strong electron density gradients occur is the mid-latitude trough. This trough is an F-region electron density depletion region a few degrees wide in latitude on the equatorward edge of the auroral oval in which the critical frequencies drop by a factor of 2-4 or more and the altitude of the electron density maximum rises by over 100 km. The mean positions of the poleward and equatorward walls of the trough and its extent in local time as a function of Kp have been calculated by means of the regression equations of Halcrow and Nisbet (1977). An example of the modelled trough positions for an equinox day is presented for various levels of geomagnetic activity. (5 pages)Oscillations of F2 layer at dawntime
http://dl-live.theiet.org/content/conferences/10.1049/cp_19940465
Introduces an index derived from a rapid run ionograms that can be used to study the local effect of travelling ionospheric disturbances (TIDs). This index describes the occurrence of ionospheric oscillation better than any other traditional parameters deduced from ionograms. Following the passage of the solar terminator, the authors detected oscillations in the gravity waves range. These oscillations were superimposed on high frequency oscillations in the acoustic wave range that also exist during the night. This confirms that the solar terminator is able to generate AGWs observable as medium scale TIDs.A propagation model for the mid and high latitude ionosphere over Europe
http://dl-live.theiet.org/content/conferences/10.1049/cp_19940470
The management of beyond line of sight HF communications depends critically on effective modelling of the ionosphere together with accurate ray tracing through it. As part of an automatic frequency management system a portable package is being developed to determine the propagation footprint of HF radio waves. The package can also be used to improve the performance of HF single site location and direction finding techniques. The package was broken up into three main sections of development, namely ionospheric specification, propagation determination and the combining of these two to provide the final HF communication model. More details of these requirements and how they are related to each other is given.Improved prediction of <i xmlns="http://pub2web.metastore.ingenta.com/ns/">I<sub>F</sub></i><sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub> and <i xmlns="http://pub2web.metastore.ingenta.com/ns/">I<sub>G</sub></i> indices using neural networks
http://dl-live.theiet.org/content/journals/10.1049/ip-map_19960575
The paper presents an investigation into the use of artificial neural networks to predict the values of the <i xmlns="http://pub2web.metastore.ingenta.com/ns/">I<sub>F</sub></i><sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub> and <i xmlns="http://pub2web.metastore.ingenta.com/ns/">I<sub>G</sub></i> ionospheric indices. Since 1982, the World Data Centre C1 for Solar-Terrestrial Physics has produced predictions for these indices using an adaptation of the McNish-Lincoln technique for predicting sunspot numbers. It is demonstrated that significantly more accurate predictions are obtained using artificial neural networks, which form the basis of predictions which will in future be issued by the World Data Centre.Large HF bearing errors for propagation paths contained within the polar cap
http://dl-live.theiet.org/content/journals/10.1049/ip-map_19971187
Large electron-density gradients in the polar-cap ionosphere, associated with the convection of patches of overdense plasma and the presence of high-latitude auroral arcs, produce tilted reflecting surfaces which result in HF signals propagating over paths well displaced from the great circle. Measurements have been made at a very high-latitude receiving site of signals propagated over paths contained within the polar cap. Systematic swings in the bearing of the received signal of up to ±100° from the great circle path were recorded and their characteristics related to the directional components of the interplanetary magnetic field and the level of geomagnetic activity, as these geomagnetic parameters play an important role in determining the state of the high-latitude ionosphere.Ionospheric forecasting technique by artificial neural network
http://dl-live.theiet.org/content/journals/10.1049/el_19981113
An artificial neural network method is applied to the development of an ionospheric forecasting technique for one hour ahead. Comparisons between the observed and predicted values of the critical frequency of the F<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub> layer, foF2, and the total electron content (TEC) are presented to show the appropriateness of the proposed technique.Simplified estimation of ray-path mirroring height for HF radiowaves reflected from the ionospheric F-region
http://dl-live.theiet.org/content/journals/10.1049/ip-f-1.1984.0020
From Milsom's equations, which describe the geometry of ray-path hops reflected from the ionospheric F-layer, algorithms for the simplified estimation of mirror-reflection height are developed. These allow for hop length and the effects of variations in underlying ionisation (via the ratio of the F2- and E-layer critical frequencies) and F2-layer peak height (via the <i xmlns="http://pub2web.metastore.ingenta.com/ns/">M</i>(3000)F2-factor). Separate algorithms are presented which are applicable to a range of signal frequencies about the FOT and to propagation at the MUF. The accuracies and complexities of the algorithms are compared with those inherent in the use of a procedure based on an equation developed by Shimazaki.Simple <i xmlns="http://pub2web.metastore.ingenta.com/ns/">M</i>-factor algorithm for improved estimation of the basic maximum usable frequency of radio waves reflected from the ionospheric F-region
http://dl-live.theiet.org/content/journals/10.1049/ip-f-1.1983.0049
The equations of Milsom are evaluated, giving the ground range and group delay of radio waves propagated via the horizontally stratified model ionosphere proposed by Bradley and Dudeney. Expressions for the ground range which allow for the effects of the underlying E- and F1-regions are used to evaluate the basic maximum usable frequency or <i xmlns="http://pub2web.metastore.ingenta.com/ns/">M</i>-factors for single F-layer hops. An algorithm for the rapid calculation of the <i xmlns="http://pub2web.metastore.ingenta.com/ns/">M</i>-factor at a given range is developed, and shown to be accurate to within 5%. The results reveal that the <i xmlns="http://pub2web.metastore.ingenta.com/ns/">M</i>(3000)F2-factor scaled from vertical-incidence ionograms using the standard URSI procedure can be up to 7.5% in error. A simple addition to the algorithm effects a correction to ionogram values to make these accurate to 0.5%.A study of F<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub> layer over Gauhati
http://dl-live.theiet.org/content/journals/10.1049/iipi.1976.0061
A study of the penetration frequency of f<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">0</sub>F<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub> and virtual height h'F<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub> of the F<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub> layer over Gauhati is made from the same data for the sunspot epoch 1968-71. It is found that the anomalous behaviour and the variation with the solar activity of the said layer follow the same pattern as in other stations of low temperate latitudes in the northern hemisphere.Use of flayer theory in ionospheric predictions
http://dl-live.theiet.org/content/journals/10.1049/piee.1971.0248
Worldwide predictions of h.f. and m.f. radio propagation conditions require extensive data on the space and time variations of ionospheric parameters such as <i xmlns="http://pub2web.metastore.ingenta.com/ns/">fo</i>F2 and <i xmlns="http://pub2web.metastore.ingenta.com/ns/">h<sub>m</sub></i>F2. Theoretical values of these parameters can be obtained by solving equations that represent the effects of various physical processes governing Flayer behaviour. The effects of winds, which are driven by the daily heating of the upper atmosphere, on the midlatitude F2layer are briefly described. Consideration is also given to the polar and the low-altitude F2layer and to problems of Flayer storms.Exact ray path calculations in a modified Bradley/Dudeney model ionosphere
http://dl-live.theiet.org/content/journals/10.1049/ip-h-2.1985.0006
Bradley and Dudeney's model of the vertical distribution of the ionospheric electron concentration consists of three distinct sections. Both the <i xmlns="http://pub2web.metastore.ingenta.com/ns/">E</i>-region and <i xmlns="http://pub2web.metastore.ingenta.com/ns/">F2</i>-region are described by parabolic variations. A linear increase is assumed to exist between the <i xmlns="http://pub2web.metastore.ingenta.com/ns/">E</i>-region peak and the <i xmlns="http://pub2web.metastore.ingenta.com/ns/">F2</i>-region. This model is currently recommended by the International Radio Consultative Committee (CCIR) for use in long-term HF sky-wave prediction work. If a slightly modified electron-concentration profile is adopted, it is possible to derive exact expressions which describe some important characteristics of oblique ray paths in the model ionosphere. Ground range, group path, phase path and apogee height can all be computed using this technique. Collisions and the effect of the earth's magnetic field are ignored. These expressions have been used for several applications where a knowledge of multipath structure on ionospheric paths is necessary.Computer procedure for deriving ionospheric characteristic M(3000)F2 from <i xmlns="http://pub2web.metastore.ingenta.com/ns/">h</i>′(<i xmlns="http://pub2web.metastore.ingenta.com/ns/">f</i>) data
http://dl-live.theiet.org/content/journals/10.1049/el_19740255
Standard procedures used at ionospheric observatories to determine the ionospheric characteristic M(3000)F2 by means of overlays or sliders applied to vertical-incidence ionograms are examined. Equations are presented to determine the corresponding values directly from numerical <i xmlns="http://pub2web.metastore.ingenta.com/ns/">h</i>′(<i xmlns="http://pub2web.metastore.ingenta.com/ns/">f</i>) data.F1 layer modelling of ionospheric electron density distribution
http://dl-live.theiet.org/content/journals/10.1049/el_19951259
As a new method to synthesise a multi-quasiparabolic (MQP) profile, the gradient of the electron density distribution of the ionosphere is used as input data. This method suits F1 layer modelling, providing a wide range of realistic shapes in the vertical ionograms by varying the gradient. Although we focus on the vertical propagation case, further simulations have shown the effect of this modelling on oblique incidence high frequency applications.